The beaches on the tourist island of Kos are as packed as ever, but it's not holidaymakers out enjoying the afternoon sun who populate the sandy shores.

Instead it's refugees, desperately fleeing a brutal conflict that has driven them from their homes in Syria.

And the mounting crisis is one of the worst the world has ever seen, according to a Dublin aid worker helping those on the Greek island.

Jane-Ann McKenna (pictured), from Foxrock, Dublin, is the director of Médecins Sans Frontières in Ireland and is currently in Kos. She says 500 migrants are arriving on "rubber dinghies and makeshift boats on a daily basis".

"The authorities here are doing their best but are just completely overwhelmed by the scale," said Ms McKenna.

Kos has effectively become a holding pen for them in their efforts to get into Europe and on to Germany.

But Ms McKenna said the island was struggling to cope.

"They have been through a difficult journey to get here and they are very anxious. They want to get to Europe and more needs to be done to help them," she said.

"The problem is, there is no reception system here and people are just left to their own devices. Looking at it, it would appear like there is a severe homeless crisis. There are people everywhere," she told the Irish Independent.

Those arriving have to be registered before they can move on to Europe, but it takes two weeks for the registration to go through. In the meantime, they must find shelter wherever they can.

"We are particularly noticing a lot of children and babies. Along the beach, there are thousands of people sleeping rough and in tents. Basically, anywhere they can find some ground to sleep on," she said.

Her teams have been giving out blankets, clothes and other aid, but she said the constant addition of more arrivals was putting strain on efforts there.

"Around 500 people are coming every day in varying conditions. They are coming on makeshift dinghies which are entirely unseaworthy," she said.

"We have been told stories of smugglers putting people on boats that are already leaking and taking on water before they have even set off. People are really desperate. They have packed their whole lives with them and their savings. They know it's risky but they need to get out."

She said that those coming on to the shore, or picked up by navy vessels on search and rescue patrols, vary in terms of their health.

But she said due to problems with sanitation and a lack of other basic services, sickness was now spreading among refugees.

Ms McKenna said the ongoing refugee crisis was the worst the world has seen since World War Two.